Babies born at below average weight are at greater risk of developmental problems, but early use of supplements may lower that risk. Low birth weight infants are more likely than normal weight babies to develop both cognitive and behavioral issues; infections during pregnancy and antibiotic use by expectant mothers can contribute to low birth weight, and premature babies may be at higher risk of falling behind in school; those weighing less than 4.5 lbs may also be five times more likely to develop some form of autism. They are also at risk for iron deficiency, which has been linked to impaired brain development.

But it wasn’t clear if treating that deficiency could help low birth weight babies avoid some of the later developmental issues associated with too little iron. Previous work found that 36% of low birth weight babies who did not take iron supplements were iron deficient at six months, compared to the 8% in the group that took 1 milligram iron supplements and the 4% in the group that took 2 milligram iron supplements.

So researchers from Sweden designed a trial to see whether treating the iron deficiency in these infants could lower their risk of developmental problems later on. They studied 285 low birth weight infants who only tipped the scales at between 4.5 – 5.5 pounds (2000 g. – 2500 g.) and were born between March 2004 and November 2007. None of the babies in the study had chronic diseases that could have affected their developmental outcome. The infants were randomly assigned to take one of three different iron supplement doses—1 mg., 2 mg., or a placebo—in the form of daily drops from the time they were six weeks old to 6 months of age. When the infants reached 3.5 years old, the scientists compared their cognitive and behavioral development to that of 95 babies with a normal birth weight.

Reporting in the journal Pediatrics, the researchers say that about 12.7% of the low birth infants who did not take iron supplements experienced behavior problems compared to 2.9% in the group that took the 1 mg. iron supplements and 2.7% in the group that was given 2 mg. supplements. Among the normal weight babies, 3.2% developed behavior problems, which suggests a four fold greater risk of behavior problems associated with low birth weight and a similar increased risk between low birth weight babies taking iron supplements v. those who are not. The researchers did not notice any significant differences in scores on the cognitive tests between the babies who took iron supplements and the ones who did not.

Even after researchers accounted for confounding factors such as the economic status of the family, age of the mother and other lifestyle influences that affect nutrition, the association between iron supplements and lower rates of behavioral problems remained significant. The authors note, however, that the babies in their study came from relatively high-income families living in a country where breastfeeding was common, so research about iron supplements’ effects on different populations is still needed. They note that the behavioral problems recorded were provided by the parents and therefore may have been biased in a way to strengthen the relationship between supplements and the health outcomes.

But even so, the fact that the infants were randomly assigned to take iron supplements strongly supports the possibility that boosting iron levels in infants who may be deficient could curb some of the developmental problems associated with being born too small. “To our knowledge, however, the current study is the first randomized trial to show a positive effect of early iron supplementation on neuro-behavioral development beyond 2 years of age,” the authors write. If confirmed, the therapy could become a relatively simple way to help low birth weight babies avoid some serious and challenging developmental problems as they age.